The overall objective of the research supported by this grant is to obtain increased knowledge about the opsonic activity of human serum and determine how this activity relates to host defense against bacterial, fungal or viral disease. These studies include assay of opsonic activity in blood stored under blood bank conditions, on changes in opsonic activity of blood from newborn infants after transfusion with adult blood and on factors which interfere with the interaction of serum opsonic factors and phagocytic cells. During this project year we intend to determine the functional maturity of opsonic and chemotactic factors in the serum of normal full-term human infants, in premature infants, an in sick infants in the intensive care nursery. Polymorphonuclear leukocyte chemotaxis, random migration from capillary tubes onto glass cover slips, glass adherence of neutrophils are the leukocyte cellular functions that will be studied. The serum will be tested in assays for the following activities: chemotaxis, bactericidal activity against E. coli and phagocytosis. In addition to these studies on newborn and sick infants there will be continuing efforts to determine the role of the "classical" or the "alternate" pathway of complement activation for activating heat-labile opsonins for bacteria and fungi in normal human serum.